CERN, Geneva
During the 2008 LHC injection synchronisation tests and the subsequent days with circulating beam, the majority of the LHC beam instrumentation systems were capable of measuring their first beam parameters. This included the two large, distributed, beam position and beam loss systems, as well as the scintillating and OTR screen systems, the fast and DC beam current transformer systems, the tune measurement system and the wire scanner system. The fast timing system was also extensively used to synchronise most of this instrumentation. This presentation will comment on the results to date, some of the issues observed and what remains to be done for the next LHC run.
DESY, Hamburg
CERN, Geneva
RIKEN/SPring-8, Hyogo
PSI, Villigen
XFELs require high precision orbit control in the long undulator sections. Due to the pulsed operation of these systems the high precision has to be reached by single bunch measurements. So far cavity BPMs achieve the required performance and will be used at the European XFEL between each of the 116 undulators. Coupling between the orthogonal planes limits the precision of beam position measurements. A first prototype build at DESY shows a coupling between orthogonal planes of about -20 dB, but the requirement is lower than -40 dB (1%). The next generation Cavity BPM was build with tighter tolerances and mechanical changes, the orthogonal coupling is measured to be lower than -43 dB. This report discusses the various observations, measurements and improvements which were done.
PSI, Villigen
ELETTRA, Basovizza
CERN, Geneva
Currently a X band traveling wave accelerator structure is fabricated in a collaboration between CERN and PSI. It will compensate nonlinearities in the longitudinal phase space at the injector prototype of the PSI-XFEL, whereas CERN will use it to test break down limits and rates in the high gradient regime. Due to the modest beam energies, the operation in the PSI-XFEL injector is quite sensitive to transverse wakes destroying the beam emittance. In that respect, the structure will use an active monitoring of the beam to structure alignment and include two wake field monitors coupling to the transverse higher order modes. These allow steering the beam to the structure axis giving a higher precision than mechanical alignment strategies. Localized offsets due to bends or tilts have individual signatures in the frequency spectrum, which in turn are correlated with different delays in the signal envelope. By taking advantage of this combined with the single bunch mode at the PSI-XFEL, the use of a relatively simple detector type RF front end should be possible, which will not only show beam offsets, but also higher order misalignments as tilts in the structure.
RIKEN/SPring-8, Hyogo
JASRI/SPring-8, Hyogo-ken
In the XFEL project at SPring-8, the resolution of a beam position monitor (BPM) is required to be less than 1 um. Therefore, we developed an rf cavity BPM (RF-BPM) to achieve a precise position resolution. The RF-BPM has two cavities: one is a TM110 cavity for position detection and the other is a TM010 cavity for phase reference and charge normalization. The resonant frequency is 4760 MHz and the loaded Q factor is approximately 50 for both cavities. The designed performance of the RF-BPM cavity was confirmed by low-level rf measurement. The rf signal is detected by an IQ demodulator to obtain the intensity and the phase. Although the BPM signal is a mixture of a position signal and a slope signal, the IQ demodulator can easily distinguish them because the phases of these signals are 90 degrees different from each other. We developed a new circuit that has small errors: the intensity error is 1 % and the phase error is 0.5 degree. The RF-BPM system has been tested by using a 250 MeV electron beam at the SCSS test accelerator. We report results of confirmed RF-BPM performances; position resolution, xy coupling, linearity, dynamic range, beam arrival timing measurements etc.
BNL, Upton, Long Island, New York
SLAC, Menlo Park, California
CERN, Geneva
We present the performance and limitations of the SPS exponential coupler for transverse instability measurements with LHC type beam. Data were acquired in 2008 in the SPS in the time domain with a bandwidth of up to 2.5 GHz. The data were filtered to extract the time evolution of transverse oscillations within the less than 5ns long LHC type bunches. We describe the data filtering techniques and reveal the limitations of the pick-up due propagating modes.
CELLS-ALBA Synchrotron, Cerdanyola del Vallès
The design of the stripline kickers shall be adapted to match the line impedance, maximize the effective beam kick, reduce the heat load and minimize the transverse coupling impedance. These kickers are used for either tune measurements or transverse feedback. We describe the ALBA design of these kickers for both Booster and Storage Ring.
Fermilab, Batavia, Illinois
LBNL, Berkeley, California
Electron cloud density in the Fermilab Main Injector was measured by observing microwave transmission along the vacuum tube. Presence of the electron cloud reduces the velocity of the microwave signal. Both frequency and time domain methods reveal relative cloud density and time evolution. The effect of beam time structure is clearly evident. The accelerator magnetic field effects the distribution of electrons making it difficult to estimate density.
MPI-K, Heidelberg
The University of Liverpool, Liverpool
This contribution describes an optical fibre sensor based on the use of a silicon photomultiplier (SiPM) composed of an array of Single Photon Avalanche Detectors (SPADs). This sensor will be used for the detection and localization of particle losses in accelerators by exploiting the Cerenkov Effect in optical fibres. As compared to conventional vacuum photomultipliers, the SPAD array allows for maximizing the geometrical efficiency of Cerenkov photon detection. The array can be directly integrated into the fibre end while retaining the same quantum efficiency (20%) in the wavelength range of interest. The SiPM is intrinsically very fast due to its small depletion region and extremely short Geiger-type discharge, which is in the order of a few hundreds of picoseconds. Therefore, the combined use of optical fibres and SiPMs seems a promising option for a modern Cherenkov detector featuring subnanosecond timing, insensitive to magnetic fields, capable of single photon detection and allowing for the possibility of realization in the form of a smart structure. We present the layout and operating principle of the detector, its characteristics, and outline possible fields of application.
DESY, Hamburg
Future accelerators like the International Linear Collider and Free-Electron Lasers require beam position measurements with resolutions between few nanometres and 1 μm. Cavity Beam Position Monitors (BPM) are able to achieve the resolution. This paper shows the basic principles of this type of monitor, followed by a brief history of the developments. Since different institutes are designing Cavity BPM system for different projects, an overview is given on their recent developments including results and limitations compared with their requirements.
ESRF, Grenoble
Until 2008, the suppression of the closed orbit distortion on the storage ring of the ESRF was obtained using two separate systems: A slow system using 224 BPM and 96 correctors performing a correction every 30 seconds, and a fast system, using only 32 BPMs and 32 correctors but working at 4.4KHz, damping the orbit distortion from 50mHz up to 150Hz; the 15mHz to 50mHz frequency span was left uncorrected. This separation of the frequency ranges of the two systems avoided cross talks between them, but prevented the efficient cancellation of the very low frequency orbit distortions caused by the frequent modification of the insertion device settings during the beamlines operation. We now coordinate the operation of the slow and fast systems and suppress this dead frequency span. This paper describes the principle and the beneficial effect of this new scheme, and its limitations. To overcome these limitations, we are now developing a single new orbit correction system which will damp the orbit distortion from DC to 150Hz; this system will use the Libera Brillance BPM electronics recently implemented at ESRF, and new fast correctors. This new scheme is also briefly presented.
Cockcroft Institute, Warrington, Cheshire
The University of Liverpool, Liverpool
The Ultra-low energy Storage Ring (USR) at the future Facility for Low-energy Antiproton and Ion Research (FLAIR) at GSI, Germany will decelerate antiproton beams of very low intensities from 300 keV down to 20 keV. Such beams can be easily disturbed by standard monitoring devices and the development of new sensitive diagnostic techniques is required. To overcome the limitations related to a very low number of particles, a low signal-to-noise ratio and ultra-low kinetic energies, a resonant capacitive pick-up has been proposed as a beam position monitor. In the planned solution, the signal gain will be realised by the use of a specially designed resonant circuit optimized to meet the requirements of the USR. The current overall design studies of the resonant capacitive pick-up, including simulations of the beam displacement sensitivity and linearity for different pick-up geometries and the equivalent resonant circuit optimisation, will be discussed.
CERN, Geneva
Carbon fibres are commonly used as moving targets in Beam Wire Scanners. Because of their thermo mechanical properties they are very resistant to particle beams. Their strength deteriorates with time due to low-cycle thermal fatigue. In case of high intensity beams this process can accelerate and in extreme cases the fibre is damaged during a scan. In this work a model describing the fibre temperature, thermionic emission and sublimation is discussed. Results are compared with fibre damage test performed on the CERN SPS beam in November 2008. For the operation of Wire Scanners with high intensity beams damage threshold are predicted.